The present invention relates to a new and improved process for fault monitoring of an electric valve containing at least two series-connected thyristors.
According to a process for fault monitoring of an electric valve such as known, for example, from the GEC Journal of Science and Technology, Vol. 48, No. 3, 1982, pp. 135-140, a 12-pulse bridge circuit for 270 kV, 1852 A (500 MW), 125 thyristors per valve are connected in series. Two 4-kV thyristors of 56 mm diameter are connected in parallel on each thyristor level. With 24 valves, the thyristor failure rate during 25 a is to be less than 0.1 per year. The triggering signals for each thyristor are transmitted via optical waveguides. The fault status of each thyristor level is indicated there by a luminescent diode. It is monitored whether the thyristors still are able to block and whether a break-over diode repeatedly responds. Such a response of the break-over diode indicates a fault in the triggering channel; the information can be transmitted to the remote control station at ground potential.
Owing to the generation of the fault status signals at high potentialand the double conversion of the signals (electrical-optical-electrical), this monitoring system is expensive and too complex, in particular for magnetically triggered valves where triggering is via pulse transformers. Optical waveguides for information transmission may break.
In thyristor protection circuits such as known, for example, from the German Company Periodical "BBC Nachrichten" (BBC News), Vol. 59, No. 3/4 (1977), pages 152 through 158, break-over diodes, so-called BOD elements are utilized.
For actuating thyristors, it is known to use a triggering pulse control unit such as known, for example, from IFAC Control In Power Electronics and Electrical Drives, Lausanne, Switzerland, 1983, pages 493 through 500, in particular page 500, FIG. 5.